Not for my wife and I, on HTC Sensation 4Gs, it doesn't.
Not quite accurate. It can be an unlocked BYOD device, but it has to be a T-Mobile-branded device.
And therein lies the rub: T-Mobile's coverage is such that many people need WiFi calling, but, to get WiFi calling, you have to accept manufacturer and carrier bloat, along with slow-to-nonexistant O/S updates.
Right now we're deciding whether to just live with it or switch carriers. It'd be too bad if we did. We like T-Mobile, but phones that don't work aren't much use.
Jim